Modulating system



Nov. 28, 1939. A. ARZMAIER I MODULATION SYSTEM Filed Jan. 8, 193aINVENITORIY ALFOMS AR MA/ER ATTORNEY Patented Nov. 28, 1939 UNITEDSTATES PATENT orr cs MODULATING SYSTEM Alfons Arzmaier,Berlin-Friedenau, Germany,

assignor to Siemens& Halske, Aktiengesellschaft, Berlin-Siemens's'tadt,Germany, a corporation of Germany Application January 8, 1938, SerialNo.183,933

v In Germany January 4,1937

3 Claims. (Cl. 178-66) ent modifications of my modulation circuit, whileFigure 2 is a potential resistance curve used 1.0 to illustrate theoperation of the rectifiers in the system.

A telegraphy arrangement. is known in the prior art in which alternatingcurrents are subject to control action by oxideor copper-type lrectifiers included in series and in shunt with the modulation circuit,while the control circuit, as

shown in Figure 1, contains a variable resistance.

In the circuit organizationknown in the earlier art, alternating currentis fed from the source I go of alternating current (of tonal frequency)through transformer 2, rectifiers i and 5 and output transformer litethe output 1. At the same time, according to the position of switch 9,direct current either positive or negative in 235 direction is sentthrough the rectifier elements by way of the change-over switch 9 whichis actuated at the rate or rythym of the telegraphic signals. Inaddition to the two copperor oxidetype rectifiers l and 5 connected inseries and 30 being in difierential relationship in reference to thealternating current, there are connected in shunt tothe system, twoadditional rectifiers ii! and ll. These last'two rectifiers also are indifierential relationship with respect to the 35 alternating current. Inthis scheme, the transmission and blocking (forward and backward)directions of the different rectifier elements are so chosen that, withthe change-over switch 9 in the position as shown in the drawing, acurrent is allowed to fiow from the positive pole of battery 8 throughthe branchoff point 22 and the resistance 3 in equal parts. throughrectifiers ill and H to the midpoint of the secondary winding of theinput transformer 2 and thence to the source of. current supply 8. Inthis positionof the switch, current is substantially blocked by A and 5so that it does not low from E2 to 25 and thence to l3. When the switch8 is shifted over to assume the position'indicated by dash lines, acurrent will be caused 'to-flow from the midpoint of the source ofcurrent 8 by way of i3 and in equal parts through the rectifiers 4 and.5 to the midpointlfi of the primary endoi the output transformer 6, andthence by I, way of 12 to the minus pole of the battery 8.

In this position of the switch current is substantially blocked by, H]and H and cannot flow from It to 3 and I2 by way of ll! and II. Inasmuchas the rectifiers when traversed by direct current in the positivedirection, exhibit a far 5 lower vresistance than when the sense ofcurrent fiow is inverse, it follows at the rate and rhythm of thetelegraphic signals; alternately the rectifiers A, 5 and Ill, H willberendered transmissive for the alternating current of generator I. In

- this manner keying of the tone frequency from I is accomplished andthe keyed'alternating current is supplied by 6 to lines I. The higherthe ratio between backward resistance and forward resistance of thevarious rectifier elements, the 15 more-completely will the alternatingcurrent coming from the generator I be modulated.

Figure 2 shows that the resistance of rectifiers such as l, 5, l0, and Hin the blocking or back-' ward direction, in the presence of a negativebiasing voltage (U) is considerably higher than at the instant when nobiasing potential (U0) is brought to act upon the said oxide rectifiers.In the presence of U1 the backward resistance attains a crest value; andin the presence of still higher values of the negative biasingpotential, the backward resistance decreases again.

New, according to the present invention, in order to improve the circuitorganization known in the prior art and as illustratedin Figure l, Icoordinate preferably a regulable resistance I3 and I4, respectively, toeach pair of rectifiers, as shownin Figure 3. Moreover, in my systemeach such additional adjustable resistance is so dimensioned that. theresistance in the backward or blocking direction of the parallelconnected rectifier pair. is thus raised by virtue of the dimensionsofthe adjustable resistances. In the case of rectifiers havingcharacteristic of a shape similar to that shown in Figure 2, this meansthat the negative biasing potential resulting from the potential drop inthe circuits including the regulable resistances lies between the valuesU0 and U1, but that it should notexceed these limits. 5. For example, if9 is in the dotted position and a current is flowing from the battery 8by way of A branch-off point It, rectifier 4, and resistance M and point12, and thence back to the saidbatter-y, then the drop of potentialoccasioned at the rectifier 4 and across the resistance M applied.across rectifier ll! acts like a blocking potential for the oxiderectifier Ill. The same situation holds good for the rectifier l l inreference to thefall'of potential-occurringacrossjrectifier 5; andresistance '55 l4. Thus, the shunting effect of IO and II is reducedconsiderably and the degree of modulation of the keyed alternatingcurrent correspondingly increased.

It is of particularly great advantage to so dimension the resistances 3and I4, according to another object of this invention, that the fall ofpotential caused across the said resistances and the correspondingrectifiers will correspond to the particular value of the negativebiasing potential at which the backward resistance attains its maximummagnitude (U1 in Figure 1).

A further improvement in an arrangement of this kind'is attainable bydividing each of the resistances S and I4 into two single resistancesl5, l6 and H, i8, respectively, as illustrated in Figure 4. For it willbe understood that, under practical conditions, it is not alwaysfeasible to. make conditions so that the characteristics and thus theresistance at the working points of the various oxide-type rectifierswill be perfectly balanced or aligned. However, by subdividing theresistances coordinated to the various rectifier pairs into smallerelements according to the invention it is possible to select for eachrectifier an optimal value of biasing potential, regardless of suchdepartures or discrepancies in the characteristics as may be present.

The subdivision of the resistances coordinated to the various pairs ofrectifiers as here suggested ofiers this additional advantage and meritthat resistances l1 and I8 may be so set that the magnetic potential orcirculation due to control current in the two portions i9 and 2E] of theoutput transformer will be exactly equal and opposite so that byconvenient setting of the resistances l1 and it all lack of symmetryliable to be occasioned as a result of dissimilarities in the oxiderectifiers 4 and 5, or as a consequence of differences in the two halvesI9 and 20 of the winding, will be compensated and neutralized. To besure, if the adjustment of the resistances I1 and i8 is eifected from aviewpoint of symmetry and alignment it will not always be possible toobtain the optimum value for the blocking potential for both pairs ofrectifiers; yet, it will be possible to adjust conditions close to theoptimal value of the said potential, without any serious disadvantagesbeing occasioned incidentally. To insure as close as possible a symmetryin the circulation through resistances i7 and I8 is of great importancesince otherwise, upon disappearance of the control direct current flow,a residual direct current component would remain in the outputtransformer 53 for each pulse of current; and the sudden disappearanceof the same occasioned upon interruption or reversal of direction of thecontrol current would set up a shock of current in the output circuit 1,with the result that current impulses are caused which are not intendedto be transmitted.

Thus, according to a still further object of the invention it issuitable to shunt or bridge resistances I! and Hi, and I and I6, bycondensers 2! and 22 for alternating current. In this manner alternatingcurrent dissipation through resistances l1, I8 and l5, l6, respectively,will be avoided, while the relation between forward resistance andbackward resistance for alternating current is greatly increased. Inthis scheme, condenser 2! becomes of particularly great importanceinasmuch as it acts upon the impedance in the forward direction of therectifiers and thus on the maximum amplitude which is transmitted, whilecondenser 22 is of lesser importance inasmuch as it merely serves todiminish the alternating current in the backward sense. This conditionapplies for low generator resistance, that is to say, constant terminalpotential. In the presence of constant circulation (that is to say, inthe presence of high inner resistance of the generator) the situation isreversed.

It is probable that a circuit organization of the kind illustrated inFigure 5 is of particularly great practical importance and value. Inthis scheme, only resistance I4 is divided into two subdivisionalresistances l1 and I8, and these are shunted by the condenser 2|.Resistance 3, on the contrary, has not been split, though it is soproportioned that for the rectifiers 4 and 5 a blocking potentialas'favorable as feasible is obtained.

According to a further object of this invention the maximum load of thecopper or oxide type rectifiers by the control direct current isregulated by a distinct resistance 23 (Figures 4 and 5) which isprovided outside the rectifier bridge arrangement rather than byresistance 3 as in the case of Figure 1. As a result the control currentloads of all rectifiers are regulated in the same measure, while theregulation of the control current will be unafiected by the dimensionsof resistances l5, E8, in fact, the setting of the latter need to beguided only by the viewpoint of insuring optimum biasing potential andsymmetry in the circulation of control direct current in the outputtransformer.

Adjustment of the alternating current amplitude ahead of the inputtransformer is efifected by the variable resistance 24. This resistancehas a high ohm valve seeing that as a general rule a plurality oftelegraph instruments are connected in parallel relation to one and thesame generator so that it becomes necessary to preelude all chances ofmutual interference between these apparatus through the joint source ofcurrent supply I.

Circuit organizations of the kind here disclosed, in contrast toarrangements known in the earlier art such as shown in Figure 1,moreover, oiTer the advantage that all of the rectifier elements arepractically subjected to the same maximum voltage, whereas in theearlier scheme the rectifiers l, 5 are subject to a considerably highervoltage than the rectifiers l0 and H. As a result, the rectifierelements may be utilized more advantageously, and the working lifethereof is extended appreciably.

I claim:.

1. In a modulator arrangement for alternating current telegraphy inwhich the alternating current impedance of two pairs of dry or oxidetype rectifiers are connected, one pair in series and the other pair inshunt with the alternating current circuit to'be controlled a source ofdirect current connected in direct current circuits with said rectifiersby polarity reversing keying means so that the direct current polaritymay be reversed at the rhythm of the signals to control the conductivityof the rectifiers at the rhythm of the signals, and an additionalresistance connected in series with each pair of rectifiers, thedimensions of said additional resistances being so chosen that thecontrol potential arising across the series pair of rectifiers and itsadditional resistance, in. the forward direction of the rectifiers, willtend to raise the blocking potential on. the shunt pair of rectifiers toa value at which said shunt pair of rectifiers are of maximum impedance.

2. In a modulator arrangement of alternating current telegrap-hy inwhich the alternating current impedance of two pairs of dry or oxidetype rectifiers are connected, one pair in series and the other pair inshunt with the alternating current circuit to be controlled, a source ofdirect current connected in direct current circuits with said rectifierby polarity reversing keying means so that the direct current polaritymay be reversed at the rhythm of the signals to control the conductivityof the rectifiers at the rhythm of the signals, an additional resistanceconnected in series with each pair of rectifiers,'the dimensions of saidadditional resistances being so chosen that the control potentialarising across the series pair of rectifiers and its additionalresistance in the forward direction of the rectifiers, will tend toraise the blocking potential on the shunt pair of rectifiers, and acondenser for lay-passing alternating currents in shunt to each of theadditional resistances.

3. In a tone keying system, a circuit having an input reactance and anoutput reactance connected in series by a pair of rectifierssubstantially symmetrically arranged in said connections, a second pairof rectifiers connected in opposition in shunt to said connections, asource of direct current, a key and pairs of contacts for connectingsaid source of direct current between symmetrical points on said outputreactance and said shunt connection and a point of symmetry on saidinput reactance and for reversing the polarity of said source ofpotential in said connection to increase and decrease respectively, theimpedance of said series rectifiers and said shunt rectifiers and viceversa, a resistance in series with said source of direct current in oneposition of said switch, the value of said resistance being such as toproduce across one of said pairs of rectifiers, a blocking potentialwhich makes its blocking impedance substantially maximum, a condenserfor Icy-passing alternating current in shunt to said resistance, andmeans for impressing alternating current to be keyed on said inputreactance.

ALF'ONS ARZMAIER.

